Glass paper



D. LABI NO GLASS PAPER originai Fil'd Sept. 17,

2 Sheets-Sheet 1 IN VENTOR oowlcK LABINO BY/MAM'. z 7" w;

ATTORNEYS April 1957 I D. LABINO 2,787,542

GLASS PAPER Original Filed Sept. 17, 1951 2 Sheets-Sheet 2 Ill SNOUOIWFIG-4 mmuummm 2,787,542 GLASS PAPER Dominick Labino, Maurnee, Ohio,assignor, by mesne assignments, to L. 0. F. Glass Fibers Company,Toledo, Ohio, a corporation of Ohio Original application September 17,1951, Serial No. 247,019. Divided and this application March 13, 1952,Serial No. 276,389

2 Claims. (CI. 92-.-3)

This invention relates to a new article of manufacture comprising glasspaper.

Paper consisting of glass fiber has heretofore been unknown in the art.Attempts made to produce glass paper have resulted in failure because ofthe lack of any tensile strength in the material produced which renderedit useless as a paper in the many uses to which paper is adapted.Further, the material produced lacked surface finish and hardness,making it unsuitable for use as paper.

However, I have discovered that fine glass fibers of uniform diameter,on the order of one micron and less, mat or felt together withself-adhesion to an extent that good tensile strength is imparted to theproduct produced and that a smooth, hard surface finish can be given tothe material, thereby making it satisfactory for use as paper. With theglass fibers having uniformity of diameter and uniformity of length,extreme uniformity of the paper is obtained.

Paper made of glass fibers according to this invention hascharacteristics that are not capable of reproduction in papers made fromnatural fibers, thus making glass paper adaptable for special purposeapplicationsin which papers made from natural fibers cannot be used. Forexample, electronic components in which insulating papers are used arelimited to a top temperature value of about 85 C., principally becauseof the destruction of the paper base of the component under heat. Thus,a paper made of glass fibers will permit of higher temperature elevationof electronic components hecfllSfi the basic fiber does not deteriorateat low temperature.

Glass paper also has a very low co'e'fiicient of expansion whicheliminates difiiculties resulting from expansion and contraction andsincethc glass fibers are nonhydroscopic, there is no change indimensional size resulting from changes in moisture content of thepaper. These characteristics are useful in the printingindustry. Also,with the glass paper [having a hard smooth surface, it is cap-able ofreceiving writing and printing.

Attempts at making papers from other synthetic fibers have resulted inproducts unsuitable for many uses'to which paper is adapted as thSyntheticfibers have required bonding, either by plasticizing the'fibersslightly, or bonding has been obtained by the use of synthetic binders.Papers of this nature, however, "are still highly susceptible todeterioration by heat or "the'bonding agent introduces a foreignsubstance into the paper whichis subject to deterioration or makesitundesirable'for use in special applications. Thebondingtogether'ofsmooth surfaced synthetic fibers has,theretore, been a substantialproblem in any attempt to produce "a "true paper from fibers other thannatural fibers.

It has been discovered, howeventhat when. glass'fibers are produced withdiameters such 'thatfthcy' approach dimensions of particles ofcolloidal'suspensions,tlratthe glass fibers when placedin'a'thinmatexhibitcharactcristics entirely different from those-exhibitedbyglass fibers of larger "diameter when placed'irr-mat'form. That PatentedApr. 2, 1357 is to say, that when glass fibers having a diameter ofabout one micron or less are arranged in a thin mat form, the fibersexhibit felting or matting characteristics and characteristics ofsurface adhesion that result in a physical interlocking of the fiberstogether to an extent that a matted or felted web of such glass fibersexhibits substantial tensile strength. This is probably brought aboutbecause of the great surface area to weight ratio of the extremely fineglass fibers. The surface area of such fine fibers in a web of anydensity is so great that there is an actual surface adhesion between thefibers. Also, this result is occasioned because of the diameter tolength ratio of the fibers wherein the length of the fiber is 500 to1000 times the diameter resulting in extreme flexibility of the fiberwhich permits it to mechanically interlock with the other fibers of likediameter and length.

Also, unlike natural fibers, glass fibers, when properly manufactured,are given the characteristics of uniform diameter and substantiallyuniform length. Thus a paper made from glass fiber of uniform diameter,and if desired, of uniform length, exhibits uniform physical, electrical and chemical characteristics as distinguished from non-uniformcharacteristics of paper made from natural fibers because of the varyingdiameter and length of the natural fibers.

It is, therefore, an object of this invention 'to produce a papercomposed of glass fibers of the character that the paper will have goodtensile strength and will have uniform physical, electrical and chemicalcharacteristics.

It is another object of the invention to produce a paper composed ofglass fibers wherein the glass fibers have the characteristic ofself-adherence providing for a paper composed exclusively of glassfiber.

It is another object of the invention to produce. a paper composed ofglass fiber in accordance with the foregoing object wherein the glassfibers of which the paper is composed have an average diameter ofsubstantially one micron or less whereby the fiber diameters approachuniformity and wherein the length of the fibers also approach(uniformity.

it is still a further object of the invention to produce a papercomposed of glass fiber in accordance with the foregoing object whereinthe diameter average of the glass fibers is held within a range of 0.1to 1.0 micron.

it is still a further object of the invention to produce a paper whereinglass fiber is the sole component, and which paper will have goodtensile strength to permit of handling of the glass paper as paper.

It is another object of the invention to provide a paper composed ofglass fiber wherein the average diameter of the glass fibers ismaintained at a selected micron size of one micron or less with a majorportion of at least 50% or over of the glass fiber being of uniform sizeat a determined micron or sub-micron diameter, the majorportion of theglass fiber being within a range of 0.3 micron of the established microndiameter.

These and other objects will be apparent from the drawings and thefollowing, description.

In the drawings:

Figure l is a diagrammatic representation of apparatus for manufacturingglass paper according to one method for its production.

Figure '2 is a cross-sectional View through the gl sn elting chamber ofthe, apparatus of Figure 1.

Figure 3 is a bottom view of the heating chamber of FigureZ.

Figure 4 is a diagrammatic representation of apparatus for producing.. glassjpaper according to a method utilizing standard-paper-makingmachinery.

Figure- 54s 'a'cross sectional view of the glass fiber collectingapparatus oi -Figure 4.

Figure 6 is a scale representing resistance of glass paper versusaverage micron diameter of the fiber.

In the manufacture of paper from natural fibers, such as those from thevarious celluloses, it is recognized in the art that a wide variation inquality of a paper product results from the unpredictable variations innatural fibers. Thus, quality control of papers made from natural fibersis one of the major factors that must be constantly watched andregulated during production of paper. This is particularly true in theproduction of papers for special applications where uniform quality andphysical characteristics of the paper must be carefully retained so asto secure as nearly as possible uniform characteristics in the productsin which the paperis used. One such example is paper products for theelectronics industry wherein the uniformity of quality of the paper,such as dielectric property, is a major factor in determining whetherthe electrical components using the paper will have uniform electricalcharacteristics. There are, of course, many other applications in whichuniform quality control of paper is a major factor.

Because of the Wide variation in the diameter and length of naturalfibers, and because of the inherent natural variation of the fibersthemselves, a wide variation in quality of the paper made from suchfibers results, such as in physical, chemical and electricalcharacteristics. The variations in the paper are carried into theelectrical components, for example, in which the paper is used, andthere is no satisfactory way to overcome the inherent natural variationsin the characteristics of the paper made from natural fibers.

A paper made from fibers having uniform diameter and length is capableof exhibiting uniform physical, chemical and electrical characteristics.Such a paper is that which can be made from glass fibers according tothis invention, the glass fibers having uniform diameter ofsubstantially one micron or less. In any paper made from such glassfibers, the average micron diameter size of the glass fiber from whichthe paper is made is preestablished and the fiber is maintained uniformat that preestablished micron or sub-micron diameter size. The averagevariation from the established micron or submicron size does not varymore than 10.45 micron, except for occasional glass fibers of somewhatlarger diameter and occasional fiber of somewhat smaller diameter.However, the average micron size is maintained within the aforementionedlimits. Preferably, the limits are carefully controlled to retain themicron size of the diameter of the glass fiber to within approximately0.3 micron from the desired and established micron or submicron size.Thus, there is established a uniformity of the diameter of the glassfiber that has heretofore been unobtainable in synthetic fibers of anykind, including glass fibers. The uniformity of the diameter of theglass fiber is a result of the manner of production of the fiber, whichwill be hereinafter described.

Glass fiber of a diameter of two micron and above are readily measurablein high-powered microscopes, but as the micron diameter of the glassfiber reduces to one micron and less, it becomes more difficult toestablish the sub-micron diameter of the glass fiber, except through theuse of electron micrographs, and the field of vision of such instrumentsis so small in relation to the length of the fibers involved that theiraverage diameter is dilficult of determination.

A standard of comparison has, therefore, been established in conjunctionwith the United States Navy Department and the Bureau of Standards bywhich the resistance per mil of thickness of a paper made from glassfiber is referenced to micron size of the fiber to establish averagesub-micron diameters of the glass fiberl Such a scale is illustrated inFigure 6.

""The scale is the result of a long series of experimental tests usingpapers made of glass fiber of increasingly small sub-micron diameter.The standard of comparison is that established by passage of 85 litersof air per minute through 100 square centimeters of a glass paper andmeasuring the resistance across the paper in millimeters of a watercolumn. The total resistance is divided by the mil thickness of thepaper to give readings of resistance per mil thickness and this is thenconverted to average fiber diameter in sub-micron size.

For example, a glass paper having a resistance of 5 millimeters of waterper mil thickness upon passage of 85 liters of air per minute through100 square centimeters of the paper has an average micron diameter sizeof the fiber established at one micron as distinguished from a paperhaving a resistance of 22.5 millimeters of water per mil thickness, thelatter having an average diameter of the glass fiber established at 0.1micron.

Electron micrograph inspection of the glass fiber of sub-micron diameterestablishes that over 50% of the glass fiber is uniform at anestablished micron diameter :0.3 micron, and with over 75% of the fiberbeing within a range of 0.45 micron with only a scattering of larger andsmaller fibers.

In the method of producing glass fibers for producing paper more fullydisclosed in my co-pending application,

Serial No. 247,010 filed September 17, 1951, now abandoned, of whichthis application is a division, the glass fiber is produced undercontrolled conditions such that the average fiber diameter is maintainedrelatively uniform within the limits established herein. Also, thelength of the glass fiber may be held to a uniform length. Hence, glasspaper made from such fiber exhibits highly uniform physical, chemicaland electrical characteristics, such as, tensile strength, chemicalresistance, and dielectric properties.

Thus, as a filtering media, paper made of glass fibers having uniformdiameter of micron size or less is superior to filter media made fromnatural fiber because of the uniformity of the interstices between theglass fibers. Because of the smallness of the interstices between theglass fibers, an extremely efficient filtering media is produced, infact one that filters smoke from the air.

The glass paper made according to this invention is highly absorbent toliquid and as a result can be saturated with various resins to give tothe paper special physical or electrical properties. In fact, suchpapers have demonstrated their ability to take up as much as twenty-onetimes their own weight of the saturating solution.

It has been discovered that glass fibers having a diameter of about onemicron or less disperse uniformly in a fluid carrier, either air orliquid, and when in the liquid, they are much the same as a colloidalsolution. Thus, a fluid carrier containing glass fibers of a diameter ofone micron or less is homogeneous in nature so that the fibers can beseparated from the fluid in a uniform homogeneous mass with resultantuniformity of density of the collected mass of glass fibers.

If the uniformity of diameter of glass fibers is not retained within theaverage limits referred to herein, the paper resulting from use of suchnon-uniform fibers exhibits the same objectionable variations inphysical, chemical and electrical characteristics as that exhibited inpapers made from natural fibers. Hence, uniformity of diameter of theglass fibers is of critical importance in the manufacture of a glasspaper having uniform physical, chemical and electrical characteristics.Preferably also, the glass fibers shall be substantially of the samelength.

Glass fibers having a diameter of one micron or less when incorporatedinto a paper exhibit the characteristic of self-adhesion, even thoughthe surface of the glass fibers is entirely smooth, resulting in a glasspaper having substantial tensile strength. This self-adhesion of theglass fibers is occasioned merely by wetting the fiber with water andcollecting the wet fiber as a web or sheet, or the fiber can becollected in dry form and thereafter wet with water. No binder whateveris necessary to secure.

theself-adhesion of the glass fibers. A papermade from fertility ofs't'riicture.

To s et i the nsi har tri iss a he glass P r t lh h r ii r made anshatters iahd d y 'ak ie stit a s i 9 t e a e ty e that i'sfiiornially d'in separa ism oi test sheets or 1 i The h t an ha it i of a stan ardYafi y W a a ma e by V l l hw i hP h A et n W sco in their sheet mold,Model G. V I

in preparing the sample sheet, the general procedure mht t s' y t h afisst an Am rica r n an ilap'enindustry, followed. Specifically,approximately two'gra "s of glass fiber is placed in about three poundsf Water a s eet n a tan d d e s a t a meets the standards oi AmericanPulp and Paper Industr ylstandards Specification IE-209 111, for tenminutes. This prepared slurry is placed in a standard sheet moldtogether W ifis h Wat to r n h w t con en o tea ho n s. hus, iving a hihlhrry s m l to that of a paper pulp. The water is then drained from theheet mo and th shout t e onds he. s t is couched oft the wire of themold. This results in a sample sheet of glass paper, approximately. tenmil in thickness a 16 3/16" is dia h i h h shee t r d a te which astandard: tensile strength. test is, made of the soprepared sheet.

Sheets prepared in this manner are those also used in tabliah hg he w tes su zm ron ia e er oic g a fibers of; which the sheet is composed ashereinbcfore des ibe It has been determined that when the averagediameter of he las fibe s from '5. to mi r n, it is n t P sible. to,produce. a paper. as there is complete disintegraicho e'ma s. of. fib rwi h noncssibili y of securin tensile. strength tests. on such mass.Such. fibers. do not eta h shee sh pe n he m f: fiber- Picked up inthe'handasiit completely. falls. apart.

When the average diameter of the. glass fiberis from 1.5 to 2.5. micron,the mass of fiber resulting from. the. making. oi a test sample, inaccordance. with the. aforementioned procedure, retains the generalsheet shape, of the. heet mold, but, the sample. cannot be. picked upman ally as there. is. insufficient tensile. strength in the sheet, tohold the. fibers together for support of the sheet sample.

However, as the average micron size-of the. glass. fiber. reducesto onemicron and. less, sheet samplesproduced in. accordance with. theaforementioned procedure exhibit tensilestren'gthsuch thata sheetcanbehand-led-manually as paperl' Eorexample, a sheet. sample. composed ofglassfiber. ofan average diameter of:. one. micronlexhibited tensilestrength. of; 0 .5 .-pou'nds.per square inch. Another. sheet samplehaving. a'veragel fiber diametenof 0.6 micronex't hib'ite'datensile.strength ofifortypounds persquare inch water wet fi er e h hi $994 tensie st es -t a t and another sample sheet having fiber diameter of an.

average or. 0.16- eiihibited: a. tensile. strength of. ninetyfour poundsperlsquare inch.

The self-adhesion is. greatly. increasedby. wettingthe fiber with anvadd water: each glass of a different glass composition and a differentalkaline content has a. critical pH valueofthe water with which itwor ksbest. 'The .elfect. of. thefcdrrectpH. value of the water Inadeacid by any'of the comrnonlacids, such as hydrochloric and sulphuric for example,is. that of ob taining a much greater and a more evendispersion ofihe.

glass fibenin thewaten Thee'ffec't is the same would'be occasioned bythe, use of a greatlyincreased quantity of water' to; disperse the sam eamou'nt ofglass. fiber. Also, a' more uniform dispersionisfobtaiiied.to.

an extent 'that less bunchingl of; the. fibers. occurs in the water andthe fibersseenito. repel.=on,e,. anothe'nwhereby each fiberiisseparatelhdispersed iathemvaterv It has. been discovered. that.

t e glass s ws??? the ri i ty of he Wat r in wh sh t e sh i i s 's at tthe n e e b r th t? from"a high a1kaline glass disperse readily in anacid water having a pH value of about 6.0, whereas the fiber made lowalkaline glass disperses in the water only when the pH value of thewater is reduced to a value in the neighborhood of 2.0. Thus the acidcontent of the, water is inversely proportional to the alkaline contentof the glass.

'Tests performed on fibers of medium alkaline content show the bestdispersion of the fiber in the water when the pH value of the water isabout 3.5. As th PH value of the water is increased to about 5.0 ordecreased to about 2.5, the. uniformity of dispersion of the fiber inthe water gradually decreases so that a pH range of approximately 2.5 isestablished relative to the; qi ical pH or the preferable pH for thewater for any glass of a particular alkalinity.

For example, in a glass having a low alkaline content, such as of sodiumor potassium, the critical pH of the water to. obtain maximum dispersionof the glass fiber is around 2.0, whereas in a glass of high alkalinecontent, containing 20%. sodiurn or potassium content for exarnpl e, thecritical pH value of the water obtaining maximum dispersion of the glassfiber in the water is about 6.0'. Thus the acid content of the water isinversely proportional to the. alkaline content of the glass. In anyevent, the pH range of the. water from the critical value'isnotmore'than 1.5 on either side of the critical V l e Tests, have shownthat when glassv fiber in the micron range is, wet with. an acid waterand. paper formed therefrom that the. tensile strength of the paper is.increased at least; threetimes. over. that wet with an ordinary tapwater over which no control, hasbeen maintained of the pH v aine in.relation to. the alkaline content of the glass.

When the fibers, are wet with a liquid they compact and felt into aself-adherent pulp-like mass which, when; dried, gir /Les. apaperproduct of good tensile strength. Also,'tlie self-adherent mass can bepressed while wet any desired pressure which increases the tensilestrength of: paper product so produced.

To."obtain glassfibers of a uniform diameter of one micron or less andretain the average diameter of the fibers within 'a range hereinreferred to, the conditions:

the glass fibersare producedare; critical after bemaintained constanttohold the sub-micron diam; eter of the fiber constant. known as staplefiber, but the length to diameter ratio is one ed gly high with.thefsub-micron diameter of; thefiber, providing. for extreme.flexibility and mechanical strength of the fiber. i

In Figures land; 2 there is illustrated an apparatus for obtainingglassfibers of onemicron indiameter or less an a Brea hin -Pap r s chfiber- In Figure 1 there is ill'us trated aheating and-melting chamberlil into which; glass marbles'are fed from a supply hopper 11-. Theglass marbles are fed into the heating and melting cha. ofr emoval ofglass from the heating and melting chain; be n Sinoethe marbles areapproximately. l zf' in diameter anddheheating and melting chamber 10 isapprox h rna tely 5" indiam'et'er, with the molten glassmassabout thelevel of; molten-glass in the heating and; melting chamber is maintainedat a constantlevel since he. m l amo t glass ede ropp ng; of. a

o f -;the marble, relative; to the, volume as the molten gl tin theheating-andmelting chamber.-

and melting-chamber 10" ismore partied larly illustratedfin Figure. 2wherein it is illustrated-as Iehash en discov red. that as t e. alkal necontent aft 5: censistingo r metal-rchamb'eri-lz ts c rcular or hatvconditions once established must" there;-

The glass fiber is of theclass;

er it! at periodic. intervals governed by. the rate 7 cylindrical inshape. The chamber 12 is preferably constructed of platinum to resistthe action of the molten glass contained within the chamber.

The bottom wall 13 of the chamber 12 contains a plurality of openings 14through which molten glass exudes from the chamber 12. These openings 14are arranged in circular rows near the periphery of the chamber 12 asillustrated in Figure 3. A heating coil 15 is placed around the exteriorof the chamber 12 and is adapted for connection to a source of highfrequency energy which may, for example, be an electronic high frequencyoscillator, or a high frequency generator. The heating coil 15 is placedsubstantially at the glass melting level of the molten glass in thechamber 12 to effect uniform heating conditions throughout the body ofthe molten glass in the heating chamber or pot 10. The heating chamber12 is preferably surrounded with a ceramic heat insulating material 16to conserve heat therein.

It has been determined over a long period of experimentation andmanufacture of glass fibers that the heating of glass by the use of ahigh frequency current in a heating coil that is placed around acircular heating chamber and positioned uniformly around the chamberresults in obtaining absolute uniformity of viscosity of the moltenglass throughout its entire mass within the heating chamber.

With the level of the molten glass maintained constant within theheating chamber 12 and with the viscosity of the molten glass absolutelyuniform throughout the entire mass thereof, thereof, there is effectedidentically the same head of glass above each opening 14 in the bottomwall of the heating chamber 12 at a viscosity of exactly the same asthat which occurs in the head of glass above every other opening in thebottom wall of the heating chamber. The head of glass above each of theopenings is exactly the same because of the parallel placement of thebottom Wall of the heating chamber relative to the level of molten glasstherein. As a result, exactly the same quantity of molten glass isexuded through each of the openings 14 from the heating chamber 12.

The head of glass above the openings 14 establishes a uniform pressuredifferential between opposite sides ofthe body of the glass to cause theglass to exude through each of the openings at a constant rate inconstant volume. However, a positive pressure can be established abovethe body of molten glass in the chamber 12 should it be desirable toobtain a flow rate of the molten glass through the openings 14 greaterthan that occasioned by the normal head.

The streams of molten glass from the chamber 12 cool quickly so thatsolidified glass fibers can be passed between the drawing rolls 17 and18 for drawing of the molten glass as it leaves the chamber 12 into thefine fibers that pass between the drawing rolls 17 and 18. The glassfibers 19 pass over a guide 20 having a recess to receive each of thefibers whereby the fibers are arranged in planar relationship for entryto between the drawing rolls 17 and 18. The drawing rolls are preferablyof a rubberlike material to frictionally engage the glass fibers 19whereby to pull them downwardly from the heating chamber 12.

The drawing rolls 17 and 18 are driven by a suitable mechanicalapparatus to rotate them at constant speed which is controlled toestablish the diameter of the drawn glass fiber 19 at a predeterminedand fixed value, for example, 0.005 to 0.007 inch.

With the flow of molten glass from the heating chamber 12 being at auniform controlled rate from each of the openings 14, and with thedrawing rolls 17 and 18 simultaneously drawing each of the moltenstrands into glass fiber from molten glass of exactly the same viscosityflowing at exactly the same rate, the drawn diameter of each of theprimary glass fibers 19 will be exactly the same within but very'minorlimits of .0005 inch.

- The primary glass fibers 19 are advanced by the drawing rolls 17 and18 over the fiat face 21 of a guide block 22 having a V-shaped edge 23.

In horizontal alignment with the V-shaped edge 23, there is provided agas burner 24 that has a horizontal discharge slot 25 through which ahigh temperature high velocity gas blast is discharged directly at theends of the glass fibers 19 below the edge 23 of the block 22. The hightemperature gas blast melts the ends of the fibers 19 and the highvelocity of the blast causes the molten glass from each of the fibers 19to be blown from the end of the fiber and simultaneously therewith drawninto a glass fiber of extremely fine diameter of one micron or less.

With the primary glass fibers 19 having a diameter of from 0.002 to0.007 inch, and with the high temperature high velocity gas blast havinga temperature of 3300 F. or higher and a velocity of 1600-2000 ft./sec.,glass fibers of 0.04 to 1.0 micron in diameter are produced.

By controlling the diameter of the primary glass fiber 19, the rate offeed, temperature and velocity of the burner gas at discharge slot 25,the diameter of the drawn staple fiber can be varied.

With the primary glass fibers 19 being fed uniformly into a burner blastof uniform temperature and velocity, the ends of the primary glassfibers are all rendered molten at the same rate with the result that thestaple fiber blown from the ends of the primary glass fibers is ofrelatively uniform length, as well as being uniform in diameter.

Thus, under controlled conditions, staple fiber having a diameter of onemicron or less can be obtained with controlled uniformity of diameterand length of the staple fiber.

The staple glass fiber thus formed is directed into a collecting hoodthat has a horizontally disposed opening 31 positioned directly above afine mesh Wire belt 32. The belt 32 is carried between rolls 33 and 34,and either of the rolls can be suitably driven whereby to drive the belt32. A suction box 35 is placed beneath the upper portion of the belt 32,and beneath the opening 31 in the hood 30, and is adapted to beconnected to any suitable apparatus for lowering the pressure in the box35.

The suction box 35 draws the fine glass fibers directed into the hoodonto the belt 32 which builds up into a loose mat 36 that is deliveredfrom the hood 30, the thickness of the mat being governed by the speedof forward advancement of the belt 32 and the rate of collection of theglass fibers on the belt.

The staple glass fiber of micron size or less uniformly disperses itselfin a fluid medium, such as, gas or liquid. This uniform dispersion ofthe glass fibers in the fluid medium results in a homogeneous flow ofthe fluid and glass fibers thereby causing uniform distribution of theglass fibers as collected upon the wire belt 32 under the hood 30. Thefinal result is that a loose mat of glass fibers of micron diameter orless is produced that is of uniform density throughout the entirestructure of the mat.

As the loose fibrous mat advances from the hood 30, a liquid spray 37,such as a water spray, is applied to the loose mat thereby condensingthe loose fibrous mat into a Wet felted mat of considerably lessthickness. The wetting of the glass fibers of micron diameter or lesscauses them to compact and felt into a homogeneous web structure tosufiicient tensile strength that the wet felted web structure supportsitself and has substantial resistance to physical separation whichallows the web to be handled in its wet condition.

The wet felted web is then treated to have the excess water removed fromit as by applying heat to the web by means of a gas burner 40 to drivethe water from the web. While in this wet condition and partially dried,the felted web 39 can be passed between press rolls to reduce thethickness of the paper thus formed.

If desired, after the paper leaves the press rolls 41 and 42, additionalheat can be applied'to the paper 43 to 9 ghsoroughly dry the same, suchas, by way of heat lamps As one example of production of glass paperaccording to the method of this invention, glass was melted in a heatingchamber at a temperature of approximately 2650 F. The primary glassfibers were drawn to a diameter from 0.002 to 0.007". These primaryglass fibers were advanced into a burner flame having a temperature ofapproximately 3300 F. with a blast velocity of 1600-2000 ft./sec.whereby staple glass fiber of a diameter of 0.04 to 1.0 micron with alength of from /s" to /3" was produced.

The staple glass fibers so produced were collected on a wire belt withthe dry loose glass fiber being collected on the belt in a mat thicknessof about /s under a suction of to 14" of water applied to the under sideof the belt in the area on which the fiber is collected. This loose webor mat of glass fibers was wet with a water spray to compact the mat toa thickness of approximately 0.005". The compacted web of glass fiberwas then heated to drive ofi excess moisture and while still damp wasdirected under a light-weight roller.

The paper produced as a result of this method had a thickness of 0.005,a density of .22 gr./cc., and a melting point of 1550 F. The paperexhibited a tensile strength in the dry condition of 220 p. s. i. and inthe wet condition of 1150 p. s. i. It will be noted that the tensilestrength of the paper is considerably greater in the wet condition thanin the dry condition, the wet strength being approximately five timesgreater than the dry strength.

The superior characteristics exhibited by paper products according tothe method of this invention is considered to be solely the result ofuniformity of diameter of glass fibers of micron diameter and less, anduniformity of length of the fibers.

In Figures 4 and 5, there is illustrated another arrangement ofapparatus for performing the method of making paper according to thisinvention wherein the staple glass fiber of micron diameter and less issupplied directly to the pulp vat or chest of a standard papermakingmachine with the result that the glass fiber is handled by thepaper-making machine in the same manner as in the production of paperfrom natural fibers, but wherein the special characteristics of theglass paper attributable to the uniformity of the glass fibers isincorporated into the glass paper.

In the arrangement of Figures 4 and 5, there is provided apparatus forproducing staple glass fiber of micron diameter and less in the samemanner as heretofore disclosed and described with reference to Figure 1.The apparatus consists of a melting chamber 30 supplied with marblesfrom a hopper 81. The primary glass fibers 82 are drawn and attenuatedby the rolls as at $3 and 89 in the same manner as heretofore disclosedand de' scribed in the corresponding apparatus of Figure l.

The primary glass fibers 82 are heated and melted by a high temperaturehigh velocity blast from the gas burner 84, causing production of stapleglass fiber of micron diameter and less in the same manner as heretoforedisclosed and described with reference to Figure 1.

The staple glass fiber of micron diameter and less so produced isdirected into a vertically-arranged hood 85 that has a battery of watersprays 86 placed therein for causing a downward spray of water onto thestapic glass fiber delivered into the hood 85. The water sprays will wetthe glass fiber and carry it downwardly through the discharge opening 87and thence into the pulp vat or chest 90 of a paper-making machine. Thegases entering the hood will exhaust upwardly from the hood, but theglass fibers will be washed from the exhausting gases by the watersprays 86. To supply sufiicient glass fiber to maintain operation of apaper-making machine, a battery of staple glass fiber producing unitsmay be 10- catcd around the hood 85 to greatly increase the quantity ofglass fiber produced and supplied to the pulp vat 90.

Water in sufiicient volume is supplied to the pulp vat and the glassfiber and water are continuously mixed by the stirrer 91 provided in thepulp vat. Since glass fiber of micron diameter and less dispersesuniformly throughout a liquid in much the same manner as colloidalparticles, a homogeneous solution of water and glass fiber flows fromthe head box 92 onto the wire 93 of a Fourdrinier type paper-makingmachine.

The wire 93 of the Fourdrinier paper-making machine passes over a vacuumbox 94 to remove excess water from the pulp on the Wire, the width ofthe web being controlled by the deckle straps 95. The pulp web formed onthe wire 93 then passes between press rolls 96 as carried on the usualendless fabric belt which thereafter carries the web over the driercylinders 97 and finally through finish press rolls 9%.

While the invention disclosed and described herein is that of thepreferred modification, yet it will be understood that thosemodifications that fall Within the scope of the appended claims areintended to be included herein.

I claim:

1. A new article of manufacture comprising a thin paper-like sheetmaterial consisting of staple glass fibers in a felted web securedtogether by self-adherence, from an acidic dispersion of glass fibers ofsubmicron diameter in which the pH characteristic is in the range of 2.0to 6.0, at least 50% of the fibers of said sheet material havingdiameters which are within :03 microns, and at least 75% of the fibersbeing within a range of :0.45 microns, the fibers having a length whichis 500 to 1000 times their diameter, said material having a tensilestrength in the dry condition sufficient to render it useful as paper.

2. A new article of manufacture comprising a thin paper-like sheetmaterial as defined in claim 1, wherein the submicron diameter fibershave a length in the range between /8 and inch.

References (fitted in the file of this patent UNiTED STATES PATENTSOTHER REFERENCES The Electrical Properties of Glass Fiber Paper, byCallinan et al., pp. 59, pub. by Naval Research Laboratory, May 1951.(Copy in Division 67.)

Electrical Manufacturing, August 1951, pages 94-97. (Copy in U. S.Patent Office Scientific Library.)

Technical News Bulletin, U. S. National Bureau of Standards, vol. 35 No.12, page 177, December 1951. (Copy in Div. 67.)

1. A NEW ARTICLE OF MANUFACTURE COMPRISING A THIN PAPER-LIKE SHEETMATERIAL CONSISTING OF STAPLE GLASS FIBERS IN A FELTED WEB SECUREDTOGETHER BY SELF-ADHERENCE, FROM AN ACIDIC DISPERSION OF GLASS FIBERS OFSUBMICRON DIAMETER IN WHICH THE PH CHARACTERISTIC IS IN THE RANGE OF 2.0TO 6.0, AT LEAST 50% OF THE FIBERS OF SHEET MATERIAL HAVING DIAMETERSWHICH ARE WITHIN $0.3 MICRONS, AND AT LEAST 75% OF THE FIBERS BEINGWITHIN A RANGE OF $0.45 MICRONS, THE FIBERS HAVING A LENGTH WHICH IS 500TO 1000 TIMES THEIR DIAMETER, SAID MATERIAL HAVING A TENSILE STRENGTH INDRY CONDITION SUFFICIENT TO RENDER IT USEFUL AS PAPER.